Preparation

Arrange the bread on a baking sheet and leave it to dry out for 3 to 4 hours or overnight.
In a large shallow dish, whisk the eggs, milk, mustard, garlic powder, and Parmesan cheese.
In a large nonstick frying pan, melt the butter over medium heat. Soak 2 slices of bread in the egg mixture, flipping to ensure both sides are coated. Transfer the bread to the frying pan. Cook until the bread becomes golden brown, about 4 minutes. Flip and cook for an additional 2 to 3 minutes. Remove from the pan and repeat until all of the French toast has been prepared.
To serve, place 2 slices of ham and 1 slice of Swiss cheese between 2 slices of French toast to make a savory sandwich. Enjoy immediately.